Photoconductive elements containing as photoconductors triarylamines substituted by active hydrogen-containing groups

ABSTRACT

Triarylamines having at least one of the aryl radicals substituted by an active hydrogen-containing group are good organic photoconductors in electrophotographic systems.

United States Patent Brantly et al.

[ 51 Apr. 25, 1972 PHOTOCONDUCTIVE ELEMENTS CONTAINING AS PHOTOCONDUCTORS TRIARYLAMINES SUBSTITUTED BY ACTIVE HYDROGEN-CONTAINING GROUPS Thomas B. Brantly; Lawrence E. Contois; Charles J. Fox, all of Rochester, NY.

Eastman Kodak Company, Rochester, NY.

Filed: Feb. 20, 1968 Appl. No.: 706,780

Inventors:

Assignee:

US. Cl ..96/l.6, 96/15, 260/576,

252/501 Int. Cl. ..G03g 5/00, 603g 7/00 Field of Search ..96/1.5; 252/501 Primary ExaminerGeorge F. Lesmes Assistant Examiner-John R. Miller AnomeyWilliam H. J. Kline, James R. Frederick and Fred L. Denson [57] ABSTRACT Triarylamines having at least one of the aryl radicals substituted by an active hydrogen-containing group are good organic photoconductors in electrophotographic systems.

18 Claims, No Drawings PHOTOCONDUCTIVE ELEMENTS CONTAINING AS PHOTOCONDUCTORS TRIARYLAMINES SUBSTITUTED BY ACTIVE HYDROGEN-CONTAINING GROUPS This invention relates to electrophotography, and in particular to photoconductive compositions and elements.

The process of xerography, as disclosed by Carlson in US. Pat. No. 2,297,691, employs an electrophotographic element comprising a support material bearing a coating of a normally insulating material whose electrical resistance varies with the amount of incident actinic radiation it receives during an imagewise exposure. The element, commonly termed a photoconductive element, is first given a uniform surface charge, generally in the dark after a suitable period of dark adaptation. It is then exposed to a pattern of actinic radiation which has the effect of differentially reducing the potential of the surface charge in accordance with the relative energy contained in various parts of the radiation pattern. The differential surface charge or electrostatic latent image remaining on the electrophotographic element is then made visible bycontacting the surface with a suitable electroscopic marking material. Such marking material or toner, whether contained in an insulating liquid or on a dry carrier, can be deposited on the exposed surface in accordance with either the charge pattern or the discharge pattern as desired. The deposited marking material can then be either permanently fixed to the surface of the sensitive element by known means such as heat, pressure, solvent vapor, or the like, ortransferred to a second element to which it can be similarly be fixed. Likewise, the electrostatic latent image can be transferred to a second element and developed there.

Various photoconductive insulating materials have been employed in the manufacture of electrophotographic elements. For example, vapors of selenium and vapors of selenium alloys deposited on a suitable support and particles of photoconductive zinc oxide held in a resinous, film-forming binder have found wide application in present-day document copying applications.

Since the introduction of electrophotography, a great many organic compounds have also been screened for their photoconductive properties. As a result, a very large number of organic compounds are known to possess some degree of photoconductivity. Many organic compounds have revealed a useful level of photoconduction and have been incorporated into photoconductive compositions. Optically clear organic photoconductorcontaining elements having desirable electrophotographic properties can be especially useful in electrophotography. Such electrophotographic elements can be exposed through a transparent base if desired, thereby providing unusual flexibility in equipment design. Such compositions, when coated as a film or layer on a suitable support also yield an element which is reusable; that is, it can be used to form subsequent images after residual toner from prior images has been removed by transfer and/or cleaning. Thus far, the selection of organic compounds for incorporation into photoconductive compositions to form electrophotographic layers has proceeded on a compound-by-compound basis. Nothing has yet been discovered from the large number of dif ferent photoconductive substances tested which permits effective prediction and therefore selection of particular compounds exhibiting the desired electrophotographic properties.

It is, therefore, an object of this invention to provide photoconductive elements for use in electrophotography containing a novel class of organic photoconductors having enhanced photosensitivity when electrically charged.

It is also an object to provide electrophotographic elements having a layer of a novel photoconductive composition which can be positively or negatively charged.

It is another object to provide novel transparent electrophotographic elements having high speed characteristics.

It is a further object of this invention to provide novel electrophotographic elements useful for producing images electrophotographically by reflex or bireflex processes.

These and other objects of this invention are accomplished with electrophotographic elements having coated thereon organic photoconductive compositions containing a tiarylamine photoconductor wherein at least one of the aryl radicals is substituted by an active hydrogen-containing group and a sensitizer for the photoconductor. Groups which contain active hydrogen are well known in the art, the definitionof this term being set forth in several textbooks such as Advanced Organic Chemistry, R. C. Fuson, pp. 154-157, John Wiley & Sons, 1950. The term active hydrogen-containing group as used herein includes those compounds encompassed by the discussion in the textbook cited above and in addition include those compounds which contain groups which are hydrolyzable to active hydrogen-containing groups. Typical active hydrogen-containing groups which are sub stituted on an aryl radical of the triarylamine according to this invention include:

a. carboxy radicals; b. hydroxy radicals; c. ethynyl radicals including substituted ethynyl radicals such as hydroxy ethynyl radicals, aryl ethynyl radicals and alkyl ethynyl radicals;

O l d) ester radicals (e.g. i10 R wherein R is an alkyl oran aryl group) e. lower alkylene hydroxy radicals (e.g., having one to eight carbon atoms);

f. carboxylic acid anhydride radicals;

g. lower alkylene carboxy radicals (e.g., having two to eight carbon atoms);

h. Acyl halide radicals (e.g.,

O H CCl etc.);

i. Arnido radicals (e.g.,

0 R ll C-N wherein R is a hydrogen atom, an alkyl group or an aryl group) j. Lower alkylidyne oxirnido radicals having 1-8 carbon atoms including substituted alkylidyne oxirnido radicals (e.g., C NOH wherein R is hydrogen or a lower alkyl radical); and

k. semicarbazono radicals; and

l. Arylene carboxy radicals including substituted arylene carboxy radicals leg,

wherein D and E are phenyl or lower alkyl radicals.

The preferred photoconductors of this invention are represented by the following structure:

carboxylic acid anhydride radical, an ester radical, a cyano radical, a semicarbazono radical, a hydroxy radical, an ethynyl radical, a methylidyne oximido radical or a phenylene carboxy radical.

The organic photoconductors of this invention exhibit substantial improvements in speed over comparable photoconductors which do not have an active hydrogen-containing group (including groups hydrolyzable to active hydrogen-containing groups). Also, those compounds in which Ar and Ar in the above formula are phenyl radicals generally have improved photoconducting properties over those which are substituted by one or two alkyl radicals. Thus, p-diphenylaminobenzoic acid generally displays higher electrical speeds than p-diethylaminobenzoic acid of p-N-methyl-N- phenylaminobenzoic acid.

Some typical photoconductors of this invention are:

TABLE I l methyl p-diphenylaminobenzoate,

ll N,N-diphenylanthranilic acid,

Ill 3-p-diphenylaminophenyl-l-propanol lV 4-acetyltriphenylamine semicarbazone,

V ethyl-2,6-diphenyl-4-(pdiphenylaminophenyl)benzoate,

VI l-(p-diphenylaminophenyl)-1-hydroxy-3- butyne,

VII 4-hydroxymethyltriphenylamine.

Vlll l-(p-diphenylaminophenyl)ethanol,

IX 4-hydroxytriphenylamine,

X Z-hydroxytriphenylamine,

ylaminobenzoic acid, XIX p-diphenylaminobenzoyl chloride,

3-p-diphenylaminophenylpropionic acid, and 4 formyltriphcnylnmine semicarbazone.

These compounds can be prepared by the methods set forth in a copending application, Ser. No. 706,799 filed concurrently herewith entitled Novel Substituted Triarylamines.

Electrophotographic elements of the invention can be prepared with these photoconducting compounds in the usual manner, i.e., by blending a dispersion or solution of a photoconductive compound together with a binder, when necessary or desirable, and coating or forming a self-supporting layer with the photoconductor-containing material. Mixtures of the photoconductors described herein can be employed. Likewise, other photoconductors known in the art can be combined with the present photoconductors. In addition, supplemental materials useful for changing the spectral sensitivity or electrophotosensitivity of the element can be added to the composition of the element when it is desirable to produce the characteristic effect of such materials.

Generally, the photoconducting compounds of this invention are not sensitive to light unless a sensitizing compound is present. While a wide variety of such substances impart spectral sensitivity to the photoconductors of this invention, it has been found that pyrylium salts, that is the pyrylium, thiapyrylium and selenapyrylium salts of U.S. Pat. No. 3,250,615, are particularly useful for sensitizing these compounds to the extent that they exhibit relatively high electrical speeds compared to those compounds which do not have an active hydrogen-containing group. Other sensitizing compounds useful with the photoconductors of the invention include tluorenes, such as 7. l 2-dioxol 3-dibenzo(a,h)-fluorene, 5,10- dioxo-4u,l ldiazodenzo(b)fluorene, 3,13-dioxo-7-oxndibcnzotb.g)fluorene, trinitrofluorenone, tetranitroflurenone and the like; aromatic nitro compounds of U.S. Pat. No. 2,610,120; anthrones of U.S. Pat. No. 2,670,285; quinones of U.S. Pat. No. 2,670,286; benzophenones of U.S. Pat. No. 2,670,287; thiazoles of U.S. Pat. No. 2,732,301; mineral acids; carboxylic acids, such as maleic acid, dichloroacetic acid, and salicylic acid; sulfonic and phosphoric acids; and various dyes such as triphenylmethane, diarylmethane, thiazine, azine, oxazine, xanthene, phthalein, acridine, azo, anthraquinone dyes.

In preparing the photoconducting layers disclosed herein, it is conventional practice to mix a suitable amount of the sensitizing compounds with the coating composition so that, after thorough mixing, the sensitizing compound is uniformly distributed throughout the desired layer of the coated element. The amount of sensitizer that can be added to a photoconductor-incorporating layer to give effective increases in speed can vary widely. The optimum concentration in any given case will vary with the specific photoconductor and sensitizing compound used. In general, substantial speed gains can be obtained where an appropriate sensitizer is added in a concentration range from about 0.0001 to about 30 percent by weight based on the weight of the film-forming coating composition. Generally, a sensitizer is added to the coating composition in an amount by weight from about 0.005 to about 5.0 percent by weight of the total coating composition.

Preferred binders for use in preparing the present photoconductive layers are film-forming polymeric binders having fairly high dielectric strength which are good electrically insulating film-forming vehicles. Materials of this type comprise styrene-butadiene copolymers; silicone resins; styrene-alkyd resins; silicone-alkyd resins; soya-alkyd resins; poly (vinyl chloride); poly(vinylidene chloride); vinylidene chloride-acrylonitrile copolymers; poly(vinyl acetate); vinyl acetate-vinyl chloride copolymers; poly(vinyl acetals), such as poly (vinyl butyral); polyacrylic and methacrylic esters, such as poly(methylmethacrylate), poly(n-butylmethacrylate), poly (isobutyl methacrylate), etc.; polystyrene; nitrated polystyrene; polymethylstyrene; isobutylene polymers; polyesters, such as poly(ethylenealkaryloxyalkylene terephthalate); phenol-formaldehyde resins; ketone resins; polyamides; polycarbonates; polythiocarbonates; poly(ethyleneglycol-co-bishydroxyethoxy phenyl propane terephthalate); nuclear substituted vinyl haloarylates such as poly(vinyl meta-bromobenzoate-co-vinyl acetate; etc. Methods of making resins of this type have been described in the prior art, for example, styrene-alkyd resins can be prepared according to the method described in U.S. Pat. Nos. 2,361,019 and 2,258,423. Suitable resins of the type contemplated for use in the photoconductive layers of the invention are sold under such trade names as Vitel PE-lO l Cymac, Piccopale 100, Saran F-220 and Lexan 105. Other types of binders which can be used in the photoconductive layers of the invention include such materials as paraffin, mineral waxes, etc.

Solvents of choice for preparing coating compositions of the present invention can include a number of solvents such as benzene, toluene, acetone, 2-butanone, chlorinated hydrocarbons, e.g., methylene chloride, ethylene chloride, etc., ethers, e.g., tetrahydrofuran, or mixtures of these solvents, etc.

In preparing the coating composition useful results are obtained where the photoconductor substance is present in an amount equal to at least about 1 weight percent ofthe coating composition. The upper limit in the amount of photoconductor substance present can be widely varied in accordance with usual practice. In those cases where a binder is employed, it is normally required that the photoconductor substance be present in an amount from about 1 weight percent ofthe coating composition to about 99 weight percent of the coating composition. A preferred weight range for the photoconductor substance in the coating composition is from about 10 weight percent to about 60 weight percent.

Coating thicknesses of the photoconductive composition on a support can vary widely. Normally, a coating in the range of about 0.001 inch to about 0.01 inch before drying is useful for the practice of this invention. The preferred range of coating thicknesses was found to be in the range from about 0.002 inch to about 0.006 inch before drying although useful results can be obtained outside of this range.

Suitable supporting materials for coating the photoconductive layers of the present invention can include any of a wide variety of electrically conducting supports, for example, paper (at a relative humidity above 20 percent); aluminum-paper laminates; metal foils such as aluminum foil, zinc foil, etc.; metal plates, such as aluminum, copper, zinc, brass, and galvanized plates; vapor deposited metal layers such as silver, nickel, or aluminum and the like. Metal (e.g., nickel, etc.) conducting layers deposited by high vacuum deposition techniques can be coated at low coverages so as to be substantially transparent to facilitate image exposure through the support. An especially useful conducting support can be prepared by coating a support material such as polyethylene terephthalate with a layer containing a semiconductor dispersed in a resin. Suitable conducting layers both with and without insulating barrier layers are described in U.S. Pat. No. 3,245,833. Other suitable conducting layers are described in U.S. Pat. No. 3,120,028. Likewise, a suitable conducting coating can be prepared from the sodium salt of a carboxyester lactone of maleic anhydride and a vinyl acetate polymer. Such kinds of conducting layers and methods for their optimum preparation and use are disclosed in U.S. Pat. Nos. 3,007,901 and 3,267,807.

The elements of the present invention can be employed in any of the well-known electrophotographic processes which require photoconductive layers. One such process is the aforementioned xerographic process. As previously explained, in a process of this type the electrophotographic element is given a blanket electrostatic charge by placing the same under a corona discharge which serves to give a uniformchargeto the surface of the photoconductive layer. This charge is retained by the layer owing to the substantial insulating property of the layer, i.e., the low conductivity of the layer in the dark. The electrostatic charge formed on the surface of the photoconducting layer is then selectively dissipated from the surface of the layer by exposure to light through an image-bearing transparency by a conventional exposure operation such as, for example, by contact-printing technique, or by lens projection of an image, etc., to form a latent image in the photoconducting layer. By exposure of the surface in this manner, a charge pattern is created by virtue of the fact that light causes the charge to be conducted away in proportion to the intensity of the illumination in a particular area. The'charge pattern remaining after exposure is then developed, i.e., rendered visible, by treatment with a medium comprising electrostatically attractable particles having optical density. The developing electrostatically attractable particles can be in the form of a dust, e.g., powder, pigment in a resinous carrier, i.e., toner, or a liquid developer may be used in which the developing particles are carried in an electrically insulating liquid carrier. Methods of development of this type are widely known and have been described in the patent literature in such patents, for example, as U.S. Pat. No. 2,297,691 and in Australian Pat. No. 212,315. In processes of electrophotographic reproduction such as in xerography, by selecting a developing particle which has as one of its components, a low-melting resin, it is possible to treat the developed photoconductive material with heat to cause the powder to adhere permanently to the surface of the photoconductive layer. in other cases, a transfer of the image formed on the photoconductive layer can be made to a second support, which would then become the final print. Techniques of the type indicated are well known in'the art and have been described in a number of U.S. and foreign patents,

such as U.S. Pat. Nos. 2,297,691 and 2,551,582, and in RCA Review," vol. (1954), page 469-484. j

The present invention is not limited to any particular mode of use of the new electrophotographic materials, and the expo sure technique, the charging method, the transfer (if any), the

developing method, and the fixing method as well as the materials used in these methods can be selected and adapted to the requirements of any particular technique.

Electrophotographic materials according to the present invention can be applied to reproduction techniques wherein different kinds of radiations, i.e., electromagnetic radiations as well as nuclear radiations, can be used. For this reason, it is pointed out herein that although materials according to the invention are mainly intended for use in connection with methods comprising an exposure, the term electrophotography wherever appearing in the description and the claims, is to be interpreted broadly and understood to comprise both xerography and xeroradiography.

The following examples are included for a further understanding of the invention.

EXAMPLE 1 Organic photoconductor 0.

5 g. Polymeric binder 1.5 g. Sensitizer 0.02 g. Methylene chloride 1 1.7 ml.

The resulting compositions are handcoated at a wet thickness of 0.004 inch on a conducting layer comprising the sodium salt ofa carboxyester lactone, such as described in U.S. Pat. No. 3,120,028 which in turn is coated on a cellulose acetate film base. The coating blocks are maintained at a temperature of F. These electrophotographic elements are charged under a positive or negative corona source until the surface potentials, as measured by an electrometer probe, reach between about 500 and 600 volts. They are then subjected to exposure from behind a stepped density gray scale to a 3,000 K. tungsten source. The exposure causes reduction of the surface potentials of the elements under each step of the gray scale from their initial potential V,,, to some lower potential V, whose exact value depends on the actual amount of exposure in metencandle-seconds received by the areas. The results of the measurements are plotted on a graph of surface potential V vs. log exposure for each step. The speed is the numerical expression of 10* multiplied by the reciprocal of the exposure in meter-candle-seconds required to reduce the 500 to 600 volt charged surface potentials to l00 volts above 0 volts. The

reduction of the surface potential to volts or below is significant in that it represents a requirement for suitable broad area development of a latent image. This speed at 100 volts is a measure of the ability to produce and henceforth to develop or otherwise utilize the latent image, higher speeds requiring less illumination to produce a latent image. When the photoconductor is absent from the coating, the surface potential does not drop to-or below 100 volts and no speed value can be assigned. This is also the case when a compound is present in the composition but is ineffective as a photoconductor. The sensitizers used are referred to below as follows:

A no sensitizer added C 2,4,7-trinitrofluorenone D crystal violet E rhodamine B F 2,4-bis(4-ethyoxyphenyl)-6-(4-n-amyloxystyryl)-pyrylium fluoborate 2,6-bis(4-ethyoxyphenyl)-4-(4-n-amyloxyphenyl)- thiapyrylium perchlorate The data in the following Table 11 represents the positive speeds at 100 volts of various compositions prepared as described above containing some of the organic photoconductors set forth in Table l. Included for comparison purposes is triphenylamine which has no active hydrogen-containing group. In each case it is noted that the photoconductive compounds of this invention show substantial improvements in speed compared to'triphenylamine. The binder employed is poly(vinyl meta-bromobenzoate-co-vinyl acetate).

TABLE ll Speed at I Volts for Sensitizer Photoconductor F H V 160 200 \'ll 200 130 ix 200 120 Triphenylamine I23 103 EXAMPLE 2 Example 1 is repeated except the photoconductive coating has the following composition:

Organic photoconductor:

p-diphenylaminobenzoic acid Binder poly(vinyl meta-bromobenzoateco-vinyl-acetate) acetate) l Sensitizer F 0. Methylene chloride 1 The 100 volt positive speed is 250. When the organic photoconductor is replaced by triphenylamine, the 100 volt positive speed is 71.

EXAMPLE 3 In order to show the ineffectiveness of sensitizing compounds other than the pyrylium, thiapyrylium and selenapyrylium salts, Example 1 is repeated using the following composition:

Photoconductor:

p-diphenylaminobenzoic acid 0.15 g. Binder:

Vitel 101* 0.50 g. Sensitizer (see Table III) 0.002 g. Dichloromethane 5.0 ml.

' A polyester of tcrephthalic acid and a mixture of ethylene glycol (1 part by weight) and 2,2-bisl4-( B-hydroxyethoxy)phenyl] propane (9 parts by weight).

The lOO volt positive speeds are set forth in Table II]. It is apparent that while some of these sensitizers impart light sensitivity to the organic photoconductor, the speed is so trivial as to have no practical effect.

TABLE III Sensitizer 100 Volt Positive Speed A C 5 D 0 E 8 EXAMPLE 4 Coating dopes prepared in the manner set forth in Example 1 containing the compounds in Table l are coated in the manner described in Example 1. In a darkened room, the surface of each of the photoconductive layers so prepared is charged to a potential of about +600 volts under a corona charger. The layer is then covered with a transparent sheet bearing a pattern of opaque and light transmitting areas and exposed to the radiation from an incandescent lamp with an illumination intensity of about 75 meter-candles for 12 seconds. The resulting electrostatic latent image is developed by conventional electrophotographic liquid developers (e.g., US. Pat. No. 2,907,674) and also by cascading over the surface of the layer a mixture of negatively charged black thermoplastic toner particles and glass beads. A good reproduction of the pattern results in each instance,

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinbefore and as defined in the appended claims.

We claim:

' 1. An electrophotographic element comprising an electrically conductive support having coated thereon a photoconductive composition comprising an electrically insulating polymeric binder, a photoconductor and a sensitizing amount of a pyrylium salt, said photoconductor having the structure:

wherein:

a. Ar, and Ar are phenyl radicals; b. Ar is an arylene radical selected from the group consisting of: l. a phenylene radical and 2. a naphthylene radical; and X is an active hydrogen-containing group selected from the group consisting of:

. a carboxy radical, an ester radical, a hydroxy radical, an alkylene hydroxy radical, an acid anhydride radical, an alkylene carboxy radical, and an acyl halide radical.

2. A photoconductive element as described in claim 1 wherein said pyrylium salt is present in an amount from about 0.005 to 5.0 percent by weight based on said photoconductive composition and said active hydrogen-containing group is a carboxy radical.

3. A photoconductive element as described in claim 1 wherein said pyrylium salt is present in an amount from about 0.005 to 5.0 percent by weight based on said photoconductive composition and said active hydrogen-containing group is an alkylene carboxy radical.

4. A photoconductive element as described in claim 1 wherein said pyrylium salt is present in an amount from about 0.005 to 5.0 percent by weight based on said photoconductive composition and said active hydrogen-containing group is an acyl halide radical.

5. A photoconductive element as described in claim I wherein said pyrylium salt is present in an amount from about 0.005 to 5.0 percent by weight based on said photoconductive composition and said active hydrogen-containing group is an ester radical.

6. An electrophotographic element comprising a conducting support having coated thereon a photoconductive composition comprising a sensitizer which is a pyrylium salt, a polymeric binder and a photoconductor selected from the group consisting of:

methyl p-diphenylaminobenzoate,

N,N-diphenylanthranilic acid,

ethyl 2,6-diphenyl-4-(p-diphenylaminophenyl)benzoate,

l-(p-diphenylaminophenyl)- l -hydroxy-3-butyne,

4-hydroxymethyltriphenylamine,

l -(p-dipheny1aminophenyl)ethanol,

3-p-diphenylaminophenylpropionic acid,

3-p-diphenylaminophenyll -propanol, 4-hydroxytriphenylamine,

2-hydroxytriphenylamine,

l-(p-diphenylaminophenyl)hexanol,

l-(p-diphenylaminophenyl)dodeconal, p-diphenylaminobenzoic acid anhydride, p-diphenylaminobenzoic acid N,N-diphenylamide, and p-diphenylaminobenzoic acid.

7. A photoconductive element for use in electrophotography comprising a conducting support having coated thereon a photoconductive composition comprising:

a. about 10 to 60 percent, by weight, based on said photoconductive composition of methyl p-diphenylaminobenzoate,

b. about 0.005 to 5.0 percent, by weight, based on said photoconductive composition of a pyrylium salt as a sensitizer, and

c. a film-forming polymeric binder for said photoconductor.

8. A photoconductive element for use in electrophotography comprising a conducting support having coated thereon a photoconductive composition comprising:

a. about 10 to 60 percent by weight based on said photoconductive composition of ethyl 2,6-diphenyl-4-(p-diphenylaminophenyl)benzoate,

b. about 0.005 to 5.0 percent by weight based on said photoconductive composition of a pyrylium salt as a sensitizer and c. a film-forming polymeric binder for said photoconductor.

9. A photoconductive element for use in electrophotography comprising a conducting support having coated thereon a photoconductive composition comprising:

a. about 10 to 60 percent by weight based on said photoconductive composition of l-(p-diphenylamino-phenyl)-lhydroxy-B-butyne,

b. about 0.005 to 5.0 percent by weight based on said photoconductive composition of a pyrylium salt at a sensitizer and c. a film-forming polymeric binder for said photoconductor.

10. A photoconductive element for use in electrophotography comprising a conducting support having coated thereon a photoconductive composition comprising:

a. about 10 to 60 percent by weight based on said photoconductive composition of 4-hydroxymethyltriphenylamine,

b. about 0.005 to 5.0 percent by weight based on said photoconductive composition of a pyrylium salt as a sensitizer and i c. a film-forming polymeric binder for said photoconductor.

11. A photoconductive element for use in electrophotography comprising a conducting support having coated thereon a photoconductive composition comprising:

a. about 10 to 60 percent by weight based on said photoconductive composition of 1-(p-diphenylaminophenyl) ethanol,

b. about 0.005 to 5.0 percent by weight based on said photoconductive composition of a pyrylium salt as a sensitizer and a film-forming polymeric binder for said photoconductor.

12. A photoconductive element for use in electrophotography comprising a conducting support having coated thereon a photoconductive composition comprising:

a. about 10 to 60 percent by weight based on said photoconductive composition of p-diphenylaminobenzoic acid,

b. about 0.005 to 5.0'percent by weight based on said photoconductive composition of a pyrylium salt as a sensitizer and I c. a film-forming polymeric binder for said photoconductor.

13. The photoconductive element of claim 7 wherein the film-forming polymeric binder is poly(vinyl metabromobenzoate-co-vinyl acetate).

14. The photoconductive element of claim 8 wherein the film-forming polymeric binder is poly( vinyl metabromobenzoate-co-vinyl acetate).

15. The photoconductive element of claim 9 wherein the film-forming polymeric binder is poly(vinyl metabromobenzoate-co-vinyl acetate).

16. The photoconductive element of claim 10 wherein the film-forming polymeric binder is poly(vinyl metaboromobenzoate-co-vinyl acetate).

17. The photoconductive element of claim 11 wherein the film-forming polymeric binder is poly(vinyl metabromobenzoate-co-vinyl acetate).

18. The photoconductive element of claim 12 wherein the film-forming polymeric binder is poly(vinyl metabromobenzoate-co-vinyl acetate). 

2. A photoconductive element as described in claim 1 wherein said pyrylium salt is present in an amount from about 0.005 to 5.0 percent by weight based on said photoconductive composition and said active hydrogen-containing group is a carboxy radical.
 2. a naphthylene radical; and c. X is an active hydrogen-containing group selected from the group consisting of:
 2. an ester radical,
 3. a hydroxy radical,
 3. A photoconductive eleMent as described in claim 1 wherein said pyrylium salt is present in an amount from about 0.005 to 5.0 percent by weight based on said photoconductive composition and said active hydrogen-containing group is an alkylene carboxy radical.
 4. A photoconductive element as described in claim 1 wherein said pyrylium salt is present in an amount from about 0.005 to 5.0 percent by weight based on said photoconductive composition and said active hydrogen-containing group is an acyl halide radical.
 4. an alkylene hydroxy radical,
 5. an acid anhydride radical,
 5. A photoconductive element as described in claim 1 wherein said pyrylium salt is present in an amount from about 0.005 to 5.0 percent by weight based on said photoconductive composition and said active hydrogen-containing group is an ester radical.
 6. An electrophotographic element comprising a conducting support having coated thereon a photoconductive composition comprising a sensitizer which is a pyrylium salt, a polymeric binder and a photoconductor selected from the group consisting of: methyl p-diphenylaminobenzoate, N,N-diphenylanthranilic acid, ethyl 2,6-diphenyl-4-(p-diphenylaminophenyl)benzoate, 1-(p-diphenylaminophenyl)-1-hydroxy-3-butyne, 4-hydroxymethyltriphenylamine, 1-(p-diphenylaminophenyl)ethanol, 3-p-diphenylaminophenylpropionic acid, 3-p-diphenylaminophenyl-1-propanol, 4-hydroxytriphenylamine, 2-hydroxytriphenylamine, 1-(p-diphenylaminophenyl)hexanol, 1-(p-diphenylaminophenyl)dodeconal, p-diphenylaminobenzoic acid anhydride, p-diphenylaminobenzoic acid N,N-diphenylamide, and p-diphenylaminobenzoic acid.
 6. an alkylene carboxy radical, and
 7. an acyl halide radical.
 7. A photoconductive element for use in electrophotography comprising a conducting support having coated thereon a photoconductive composition comprising: a. about 10 to 60 percent, by weight, based on said photoconductive composition of methyl p-diphenylaminobenzoate, b. about 0.005 to 5.0 percent, by weight, based on said photoconductive composition of a pyrylium salt as a sensitizer, and c. a film-forming polymeric binder for said photoconductor.
 8. A photoconductive element for use in electrophotography comprising a conducting support having coated thereon a photoconductive composition comprising: a. about 10 to 60 percent by weight based on said photoconductive composition of ethyl 2,6-diphenyl-4-(p-diphenylaminophenyl)benzoate, b. about 0.005 to 5.0 percent by weight based on said photoconductive composition of a pyrylium salt as a sensitizer and c. a film-forming polymeric binder for said photoconductor.
 9. A photoconductive element for use in electrophotography comprising a conducting support having coated thereon a photoconductive composition comprising: a. about 10 to 60 percent by weight based on said photoconductive composition of 1-(p-diphenylamino-phenyl)-1-hydroxy-3-butyne, b. about 0.005 to 5.0 percent by weight based on said photoconductive composition of a pyrylium salt at a sensitizer and c. a film-forming polymeric binder for said photoconductor.
 10. A photoconductive element for use in electrophotography comprising a conducting support having coated thereon a photoconductive composition comprising: a. about 10 to 60 percent by weight based on said photoconductive composition of 4-hydroxymethyltriphenylamine, b. about 0.005 to 5.0 percent by weight based on said photoconductive composition of a pyrylium salt as a sensitizer and c. a film-forming polymeric binder for said photoconductor.
 11. A photoconductive element for use in electrophotography comprising a conducting support having coated thereon a photoconductive composition comprising: a. about 10 to 60 percent by weight based on said photoconductive composition of 1-(p-diphenylaminophenyl) ethanol, b. about 0.005 to 5.0 percent by weight based on said photoconductive composition of a pyrylium salt as a sensitizer and a film-forming polymeric binder for said photoconductor.
 12. A photoconductive element for use in electrophotography comprising a conducting support having coated thereon a photoconductive composition comprising: a. about 10 to 60 percent by weight based on said photoconductive composition of p-diphenylaminobenzoic acid, b. about 0.005 to 5.0 percent by weight based on said photoconductive composition of a pyrylium salt as a sensitizer and c. a film-forming polymeric binder for said photoconductor.
 13. The photoconductive element of claim 7 wherein the film-forming polymeric binder is poly(vinyl meta-bromobenzoate-co-vinyl acetate).
 14. The photoconductive element of claim 8 wherein the film-forming polymeric binder is poly(vinyl meta-bromobenzoate-co-vinyl acetate).
 15. The photoconductive element of claim 9 wherein the film-forming polymeric binder is poly(vinyl meta-bromobenzoate-co-vinyl acetate).
 16. The photoconductive element of claim 10 wherein the film-forming polymeric binder is poly(vinyl meta-boromobenzoate-co-vinyl acetate).
 17. The photoconductive element of claim 11 wherein the film-forming polymeric binder is poly(vinyl meta-bromobenzoate-co-vinyl acetate).
 18. The photoconductive element of claim 12 wherein the film-forming polymeric binder is poly(vinyl meta-bromobenzoate-co-vinyl acetate). 